We examined psychometric properties of a Modified Physical Activity Questionnaire for Children (MPAQ-C). Thirty-two parents (Study 1), 40 students (6-9 years) and one of each student's parents (Study 2), and 625 parents (Study 3) completed the MPAQ-C. The MPAQ-C (six items) measured children's physical activity (PA) after school, and during evenings and weekends for 7 days. Test-retest reliability (Study 1) and convergent validity (Study 2) were measured. Factor validity of the MPAQ-C (Study 3) was examined using confirmatory factor analysis. A single-factor model of the MPAQ-C fit the data well (?[superscript 2] (9) = 42.78, p < 0.001; comparative fit index [CFI] = 0.977; non-normed fit index [NNFI] = 0.962; root mean square error of approximation [RMSEA] = 0.079 [90% confidence interval {CI} = 0.057 to 0.11]), with good test-retest reliability, composite reliability (0.80) and convergent validity. The factor loadings of MPAQ-C were invariant across fathers/mothers (??[superscript 2] (6) = 3.44, p > 0.05). The MPAQ-C is a suitable parent proxy for measuring young Chinese children's PA.